统一架构第8部分:数据访问

[中文适用范围]： 本部分IEC 62541是整体OPC统一架构（OPC UA）标准系列的一部分，定义了与数据访问（DA）相关联的信息模型。它特别包括额外的变量类型以及对数据访问所需的节点类和属性的补充描述、额外属性以及其他信息和行为。完整的地址空间模型（包括所有节点类和属性）在IEC 62541-3中规定。检测和数据访问的服务在IEC 62541-4中规定。 [外文原描述]： IEC 62541-8:2020 is part of the overall OPC Unified Architecture (OPC UA) standard series and defines the information model associated with Data Access (DA). It particularly includes additional VariableTypes and complementary descriptions of the NodeClasses and Attributes needed for Data Access, additional Properties, and other information and behaviour. The complete address space model, including all NodeClasses and Attributes is specified in IEC 62541-3. The services to detect and access data are specified in IEC 62541-4. This third edition cancels and replaces the second edition published in 2015. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) added new VariableTypes for AnalogItems; b) added an Annex that specifies a recommended mapping of OPC UA Dataccess to OPC COM DataAccess; c) changed the ambiguous description of "Bad_NotConnected"; d) updated description for EUInformation to refer to latest revision of UNCEFACT units.